關於光污染 About light pollution
「光污染」（又稱光害）是一種因過度使用人為室外照明，而對自然環境和生態等引起的負面影響。人為室外照明包括街燈、霓虹招牌、廣告版照明等。光污染不單令我們失去美麗的星空，更破壞大自然及人類的生活環境，亦浪費能源。
“Light Pollution” is a form of environmental degradation in which excessive artificial outdoor lighting, such as street lamps, neon signs, and illuminated signboards, affect the natural environment and the ecosystem. Light pollution not only rids us of the starry night sky, it also indicates a waste of electric energy and damages the natural and our living environment.

星空保育 Dark sky conservation
過量或設計不良的室外照明光線，會從地面直射或反射上天空，再經大氣中的雲、霧和污染物（如懸浮粒子等）散射至大範圍，導致一大片的夜空被照亮，夜空中可見星星的數目因而減少。
The wasteful light emitted directly upwards or reflected upwards from excessive and poorly-designed artificial light sources can be scattered to a wide area by the cloud, fog, and pollutants like suspended particulates in the atmosphere. A wide patch of the night sky is thus brightened, leading to a reduced number of stars visible due to a reduction of the light contrast in the sky.

星空是各個民族的共同文化遺產，也是生活的重要部份。我們正面臨星空持續地消失的威脅，這是地球需要面對的環境挑戰之一。星空保育是指保護黑夜環境，讓人類和動植物享有不受污染的黑夜。
The night sky is not only a common cultural heritage of all mankind but also an important part of our life. We are under a severe threat of the disappearing starry night, which is just another component of the environmental challenge the Earth faces. Dark sky conservation is the protection of our starry night sky and the preservation of our naturally dark sky, for the benefits of all humans, fauna and flora.

香港大學光污染研究 HKU light pollution research
香港大學物理系於2003年開始進行光污染研究。研究團隊建立了「香港夜空光度監測網絡」，自2010年5月起測量各區光污染情況，共收集了超過二千萬個夜空光度數據，數據量冠絕全球。研究團隊分析所收集的夜空光度數據，發現市區在晚上8時半至11時的夜空光度比國際標凖光亮100至1,000 倍，即使於較為徧遠的環境（如濕地公園），仍比標凖光亮100倍以上。香港成為全球光污染最嚴重的地方之一。
HKU Department of Physics has been conducting light pollution research since 2003. The research team built the “Hong Kong Night Sky Brightness Monitoring Network” in May 2010. Since then, the network has monitored the light pollution conditions in different parts of Hong Kong and collected more than twenty million night sky brightness data. By analysing this world’s largest dataset, researchers found that the Hong Kong urban night sky to be 100 to 1,000 times brighter than the international dark sky standard between 8:30pm and 11:00pm. Even in remote locations such as the Wetland Park, the night sky there was above 100 times brighter than the standard. Hong Kong becomes one of the most light-polluted cities in the world.

研究團隊還發現，當公共設施和商業照明陸續地關上時，夜空光度亦逐步遞減。位於市區的監測站，在每天晚上11時、凌晨0時和凌晨1時，都錄得大幅度的夜空光度下跌，與眾多人為燈光的使用模式符合，證明人為室外燈光是光污染的元凶。
The research team also found that the night sky dims progressively when public and commercial lightings are being turned off at night. For example, the urban sky showed sudden dimming near 11pm, 12am, and 1am every night, likely caused by the timing patterns of the nearby outdoor lighting. This no doubt proves that human lighting is the source of light pollution.

全球光污染監測 Global light pollution monitoring
近年，港大的光污染研究團隊將夜空光度監測技術推廣至外地，建立了「Globe at Night – Sky Brightness Monitoring Network」。這個全球性網絡目前有23個監測站，分布在亞洲、歐洲和非洲的9個國家或地區。研究項目的網站提供了監測站的資料和實時數據。
The HKU light pollution research team recently introduced our monitoring techniques internationally by establishing the “Globe at Night – Sky Brightness Monitoring Network project”. This global network currently has 23 stations operating in 9 countries/regions in Asia, Europe, and Africa. Details of the survey and the real-time data from around the world can be found in the project website.

經初步分析，數據顯示世界各地的夜空光度差別顯著，最光的地區位處市區，最黑暗的地區位處原始國家公園。各地的市區夜空亦普遍因每晚燈光使用量的減少而逐步轉暗，情況與香港相約。數據亦顯示郊區監測站所錄得的夜空光度，在整晚大致保持平穩，反映出人為燈光使用的影響較低。
Preliminary analysis of the data shows that there are large variations in night sky brightness worldwide: urban night skies are significantly brighter than night skies in pristine national parks. In general, in urban areas the night skies get progressively darker with time as the light usages by humans decrease over the night. The situation is similar to that observed in Hong Kong. On the other hand, rural stations show steady sky brightness throughout the night, reflecting low effect of human light usages.

如何減少光污染？智慧地使用照明 How to reduce light pollution? Use lighting wisely減少使用不必要的室外照明 Reducing abuse of outdoor lightings
原則是合理地運用照明：不要加設非必要的照明，和關掉非使用中的照明。離開房間時順手把燈關掉，也可以簡單地達到目標。從城市的角度來看，在深夜時關掉或調暗街上的霓虹廣告招牌、球場的泛光燈、郊野公園範圍內的街燈、大橋裝飾的燈泡等，都是可以減少光污染的方法。
The rule of thumb is using lighting reasonably: do not set up unnecessary lighting and turn off lights which are not in use. Turning off the light when you leave a room can also help. From the perspective of the entire metropolis, turning off and dimming the neon signboards on the streets, floodlight on sport grounds, road lights in country parks and decorative lights on bridges are all possible ways to alleviate light pollution.

改裝現有的室外照明 Modifying existing lightings
大部分室外照明的設計並不有利於減少光污染。燈罩設計不良，令部分光線向上照耀。這些光線沒有實質作用，既浪費能源，也增加光污染。優良的「截光型燈具」設計，將光線聚焦並向下照射，盡量消除向天照耀的光線，減少光污染。
A majority of the outdoor lighting currently installed are not dark-sky friendly, in which a significant portion of the emitted light is spread over a wide area and not concentrated in the targeted area. Upward-directed light is particularly useless and wasteful, and is a major culprit of light pollution. The improved “Full CutOff ” design limits the spreading of light and focuses the light downward, minimising light pollution.

選用有利天文觀測的光源 Choosing astronomical-friendly lighting sources
高壓鈉燈和光管是最影響天文觀測的照明。而低壓鈉燈則是對天文觀測造成較少影響的光源，它所發射的光線只有小部分在可見光譜中，天文學家只需用濾鏡便能輕易地將此除去。
Unlike the high pressure sodium lamps and fluorescent lamps, low pressure sodium lamps are least affecting with regard to astronomical observations. It is because the emission spectrum of low pressure sodium lamps occupies a relatively small portion of the entire visible spectrum, and astronomers can easily filter out its contributions by applying filters.